How much effort do you put into the initial "hook" linking PC's to your adventure?
The near-minimum would be having them be hired by an NPC to do a job.
Near-maximum would be something akin to a PC wanting revenge for his slain parent, lover, pet, etc.
Note: yes, I know some people are huge proponents of the sandbox/do whatever you want game. I allow my PC's to do whatever they want but I try to create events that resonate with their characters' desires, backgrounds, goals, etc.
Keep in mind the 7 basic "conflicts" of storytelling...Put another way, I think, any of these could be transposed into the RPG world as the ever elusive "hooks."
Character (i.e."the Party") v. Self
Character v. Character
Character v. Society
Character v. Nature
Character v. the Supernatural
Character v. Destiny (a.k.a. "Fate v. Freewill")
That said, I think your "range" of "near-min"=Hired by NPC and "near-max"=personal connection to an NPC is a bit limiting.
1. "Help Wanted" a.k.a. "Hired by NPC to do a job." It's simple, clean, and can get you into as easy or complex an adventure/campaign as you like.
These sorts of hooks can be anything from the "destitute farmer" calling for aid to the mayor looking for some added "muscle" since the town guard can't be spared to the ever-popular (and possibly most generic) wealthy and most likely "mysterious" stranger/artistocrat/merchant/local wizard looking for some help with an "errand", protection/defense, or to take on something "under the radar" of the local gendarme.
2. "PC Phone Home": I don't know that "wanting revenge" would really be the "near-max" for me. That falls somewhere in the middle, I'd say. It would fall under the umbrella of the "More Personal PC Connection" hook...which could very easily be in conjunction with #1...except instead of answering a bulletin for the town or meeting some stranger in an inn it is an NPC with a closer connection to a (or multiple) PC: family member, mentor/teacher, childhood friend, past (or current) romantic interest.
These are all sorts of the same "hook." Motivations could be love, jealousy, ego/pride (up to and including hubris), "familial obligation", revenge, etc. etc. across the spectrum of human(oid) emotion. So I wouldn't necessarily say it is the "max" of hooks...if "max"=PC emotional resonance or personal connection, then perhaps.
3. "Park Ranger": There's a fell beast tearing up the countryside. The UberGreen Forest has turned Red. The river has become tainted. Last night, the crops all uprooted themselves and walked away. The Livestock have taken over Joe Overalls farm and are revolting against the rest of the village. Handle it! This leads to the investigation...Where'd it come from? Why's it there? Is it actually evil/out to destroy everyone or just migrating? Protecting its territory? Its young? Is it wounded/acting out of pain? (Lion with a thorn in it's paw, anyone?)
This doesn't rely on hooks 1 or 2, though certainly
could be a task set forth by an NPC. But it doesn't have to be. The party comes across the creature, forest, field, river, etc...on their own or sees some damage/death it has wrought and decides to seek out the cause/a solution.
4. "You're Off to See the Wizard": The party needs to get from town A to city B because <insert potential plot device here>. The reason they have to go can be anything and is actually secondary (if not completely irrelevant) to the adventure.
The "plot" is actually the story that happens en route....But the HOOK that gets them on the road in the first place is having to get to B.
5. "Here They Come to Save the Day": This could be as local as "rescue the princess from the evil baron before the ritual" to as encompassing as "find the artifact/slay the god before the multiverse unravels" or...ya know..."Destroy the One Ring."
If you have a party of "would-be heroes" and "do-gooders" then in whatever fashion you like and can be as personal as a prophetic poetry of one PCs destiny to a long series of adventures to find the clues themselves, whatever...tell them: "Apocalypse. Next Tuesday. Unless you can..."
Actually, this works better WITHOUT a timetable to begin with...then, about half way through, maybe even by their own actions, you introduce/throw it at them that "Oh yeah. Did I mention, that Apocalypse now looks like it'll happen next Tuesday." PC's LOVE that!
If that doesn't hook them...then I dunno what will...I guess this is what I would consider the "max" for plot hooks...since there's really not a lot else going on if the world comes to an end.
Ummm...I think that's all I have for now.
Have fun and happy hooking...

wait, that doesn't sound quite right.
--Steel Dragons